This invention relates to a lock structure for a box which is applied to a box such as an electric connection box mounted on a vehicle or an exterior box for receiving it.
As a box lock structure of this type, various structures have heretofore been proposed. A first related technique is shown in FIGS. 7 and 8.
In FIGS. 7 and 8, a retaining projection 101 is formed on an inner side surface of an upper cover 100. An elastic retaining arm 103 is formed in an upstanding manner at a side wall of a lower cover 102, and a distal end retaining portion 103a is formed in a projecting manner at a distal end of this elastic retaining arm 103.
In the above construction, when the upper cover 100 and the lower cover 102 are assembled together, the elastic retaining arm 103 is moved in a locking direction. With this movement, first, the distal end retaining portion 103a of the elastic retaining arm 103 is brought into abutting engagement with the retaining projection 101, and the elastic retaining arm 103 is elastically bent and deformed, so that the distal end retaining portion 103a passes over the retaining projection 101. When the distal end retaining portion 103a moves to a position where it completely passes over the retaining projection 101, the elastic retaining arm 103 is bent and restoringly deformed, so that the distal end retaining portion 103a is retained by the retaining projection 101. With the foregoing, a locked condition is established between the upper cover 100 and the lower cover 102.
In the lock structure of this first related technique, when a high lock canceling force acts on the elastic retaining arm 103 in the locked position to elastically bend and deform the elastic retaining arm 103, the lock is canceled. Therefore, the lock retaining force depends only on the elastic restoring force of the elastic retaining arm 103.
Also, in order to form the first related technique into a structure in which the lock is made even a little harder to be canceled, a lock structure of a second related technique shown in FIGS. 9 to 11 has been proposed.
As shown in FIGS. 9 to 11, in the lock structure of this second related technique, an arm restraint rib 104 is formed on an inner surface of an upper wall of an upper cover 100. This arm restraint rib 104 is disposed at a rear side of an elastic retaining arm 103 which is to be retained by a retaining projection 101. When a height of the retaining projection 101 is represented by d, and a gap between the arm restraint rib 104 and the elastic retaining arm 103 located in a locked position is represented by D, the position of the arm restraint rib 104 is set such that d<D is established. Therefore, in the process of movement of the elastic retaining arm 103 in a locking direction, a distal end retaining portion 103a of the elastic retaining arm 103 can pass over the retaining projection 101 without interference by the arm restraint rib 104 as shown in FIG. 10.
In the lock structure of this second related technique, the elastic retaining arm 103 located in the locked position can not be shifted in a large amount in an elastically-bending direction as shown in FIG. 11, and therefore in this structure, the lock is harder to be canceled as compared with the first related technique. Further, the following publication exists as the prior art.
[Patent Literature 1] JP-A-5-147665
However, even in the lock structure of the second related technique, the lock retaining force basically depends only on the elastic restoring force of the elastic retaining arm 103, and therefore this structure has not sufficiently met the requirement that the lock should be made hard to be canceled.
Here, if the position of the arm restraint rib 104 is set such that d>D is established, the lock retaining force can be enhanced, but in this structure, in the process of movement of the elastic retaining arm 103 in the locking direction, the distal end retaining portion 103a of the elastic retaining arm 103 interferes with the arm restraint rib 104, and can not pass over the retaining projection 101.